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•    '  "^  ^,^  J    ■  With  the  writers  Compliments. 

yl    I     I    II     T  m>    I7|i»i<>.       - 


EXPERIMENTAL  RESEARCHES  ON  THE 
TENSION  OF  THE  VOCAL  BANDS. 

{a) — THE  ACTION   OF  THE   THYRO-CRICOID    MUSCLE. 
(/^)— THE    ACTION   OF    THE    EXPIRATORY    BLAST   OF   AIR. 


F.    H.   HOOPER,   M.D. 


ASSISTANT    PHYSICIAN   TO    THE   CLINIC  FOR  DISEASES   OF  THE    THROAT,    MAS- 
SACHUSETTS  GENERAL  HOSPITAL  ;    FELLOW   OF  THE  AMERICAN 
LARYNGOLOGICAL    ASSOCIATION,    ETC. 


COLUMBIA  UNIVERSITY 

DEPARTMENT  OF  PHYSlOLOf^V 

College  of  Phywciahs  amd  SuRssoNa 

4»7  WEST  FIFTY  *INtH  STRtET 

WEW  yowc 


j  h^yn  U<-^^  C^-CkJL. 


QP5dL> 


EXPERIMENTAL    RESEARCHES    ON    THE    TEN- 
SION  OF  THE  VOCAL  BANDS. 

{a). THE    ACTION    OF    THE    THYRO-CRICOID    MUSCLE. 

(<5). THE    ACTION    OF    THE    EXPIRATORY    BLAST    OF    AIR. 

By  F.  H.  hooper,  M.D,,  Boston, 

ASSISTANT   PHYSICIAN   TO  THE   CLINIC   FOR  DISEASES  OF  THE  THROAT,  MASSACHUSETTS  GENERAI. 
HOSPITAL  ;     FELLOW   OF  THE  AMERICAN   LARYNGOLOGICAL   ASSOCIATION,    ETC. 

THE  experiments  recorded  in  this  paper  were  per- 
formed in  the  physiological  laboratory  of  the  Har- 
vard Medical  School,  in  conjunction  with  Professor  Henry 
P.  Bowditch. 

The  diagrams  and  figures  contained  in  the  text  were  re- 
■produced  from  the  original  tracings  and  drawings  by  the 
■photo-electrotype  engraving  process. 

(^a). — THE   ACTION   OF   THE   THYRO-CRICOID    MUSCLE. 

Although  the  literature  pertaining  to  the  function  of  this 
important  tensor — commonly  but  incorrectly  called  the 
crico-thyroid  muscle — is  not  extensive,  it  furnishes  us  with 
every  possible  variety  of  opinion.  The  muscle  is  usually 
described  as  arising  from  the  front  and  lateral  part  of  th«a 
cricoid  cartilage  ;  its  fibres  pass  upward  and  outward,  diverg- 
ing slightly,  and  are  inserted  into  the  inferior  and  inner 
border  of  the  thyroid  cartilage  from  near  the  median  line 
in  front,  and  as  far  back  as  the  anterior  border  of  its  lower 
cornu.  Its  nervous  supply  comes  principally  from  the  ex- 
ternal branch  of  the  superior  laryngeal  nerve. 

The  observers  who  have  directed  their  attention  to  its 
action  may  be  divided  into  six  classes: — 

I 


^^bar 


2  F.    II.   HOOPER. 

I.  Those  who  hold  that  it  tilts  the  thyroid  cartilage 
downward  and  forward  on  to  the  cricoid.  (This  is  the  gen- 
erally received  theory  in  regard  to  it,  and  is  the  view  ex- 
pressed in  such  standard  works  of  anatomy  and  physiology 
— with  the  exception  of  the  ninth  edition  of  Quain,  which 
has  only  recently  appeared — as  Galen,  Casserius,  Gray,  Hyrtl, 
Henle,  Meyer,  Meckel,  Hartmann,  Cruveilhier,  Sappey, 
Morel  et  Duval,  Carpenter,  Huxley,  Todd  and  Bowman, 
Foster,  Hermann,  and  others;  and  among  laryngologists, 
Tiirck,  Stoerk,  Mackenzie,  Schrotter,  and  Seiler.) 

H.  Those  who  affirm  that  it  draws  the  cricoid  up  on  to 
the  thyroid.  (Cowper,  1724;  Magendie,  1813;  Lauth,  1835; 
Bishop,  1839;  Longet,  1841  ;  Cuvier,  1846;  Harless,  1853  '■> 
Battaille,  1861  ;  Fourni^,  1866;  Jelenffy,  1873;  Schech, 
1873;  Schmidt,  1873;  Milne  Edwards,  1876;  Cohen,  1880; 
Elsberg,  1882  ;  Quain's  Anat.,  9th  ed.) 

HI.  Those  who  maintain  that  it  draws  both  cartilages 
together  by  its  contraction,  the  predominance  of  movement 
being  in  the  thyroid.  (Vesalius,  Merkel,  Theile,  B^ciard, 
Harrison.) 

IV.  Those  who  assert  that  its  action  is  according  to  the 
fixation  of  the  cartilages  ;  that  when  the  cricoid  is  the  point 
fixed,  the  thyroid  is  the  one  moved,  and  vice  versa.  (Budge, 
Riegel,  Mandl.) 

V.  Those  who  insist  that  instead  of  drawing  the  car- 
tilages together,  its  function  is  to  retain  them  in  a  fixed 
position  when  separated.     (Vierordt,  Luschka.) 

VI.  The  sixth  class  is  purely  of  historical  interest. 
Brown  (1683)  stated  that  "when  the  muscle  is  contracted, 
it  extends  the  cartilage  cricois,  or  annularis,  and  so  openeth 
its  cleft  for  a  more  deep  and  greater  voice  or  sound." 
Dionis  (1695)  considered  that  its  action  was  to  dilate  the 
sides  of  the  thyroid,  thereby  enlarging  the  glottis.  Haller 
(1766)  agreed  with  this  view,  but  thought  also  that  it  ap- 
proximated the  two  cartilages. 

But  one  explanation  can  be  offered  to  account  for  these 
conflicting  theories.  Except  in  the  case  of  four  observers 
(Magendie,  Longet,  Schech,  Schmidt),  the  above  hy- 
potheses were  not  founded  upon  experimentation.     They 


TENSION  OF   THE    VOCAL   BANDS.  3 

are  mere  speculations  unsupported  by  reliable  experimental 
proof.  And  it  is  a  significant  fact  that  the  four  observers 
named — the  only  ones  who  substantiated  their  opinions  by 
experiments  upon  animals — all  agree  concerning  the  action 
of  the  muscle. 

Magendie  in  1813  not  only  gave  a  very  clear  description  of 
the  distribution  of  the  laryngeal  nerves,  but  he  was  the  first, 
by  experimentation,  to  observe  and  record  the  true  action 
of  the  thyro-cricoid  muscle.  He  fails  to  tell  us  upon  what 
animal  he  made  his  observation,  and  contents  himself  with 
saying:  "  Quand  on  enleve  la  peau  du  col,  de  maniere  a 
apercevoir  1'  intervalle  crico-thyroi'dien,  on  a  lieu  de  se  con- 
vaincre  que  dans  la  production  des  son  aigus,  et  surtout  a 
r  instant  de  la  deglutition,  le  cartilage  cricoide  s'  eleve  au 
point  que  son  bord  superieur  s'  engage  sous  le  bord  inferieur 
du  cartilage  thyroide." 

We  find  mentioned,  however,  in  Cowper  (1724),  that  the 
function  of  the  muscle  "  is  to  pull  up  the  annularis  rather 
than  to  bring  down  the  scutiformis." 

Our  own  experiments,  performed  in  a  different  manner 
from  any  hitherto  recorded,  result,  we  think,  in  definitely 
determining  the  chief  effect  produced  upon  the  cartilages  by 
the  contraction  of  the  muscle.  They  prove  the  accuracy 
of  Magendie's  early  observation,  and  force  us  to  reject  the 
theory,  so  generally  accepted,  that  the  thyroid  cartilage  is 
drawn  down  by  its  influence.  The  dogs  used  in  the  investi- 
gations were  prepared  as  follows : 

The  animal  being  thoroughly  etherized  and  secured  to  a 
dog-holder  on  a  table,  both  superior  laryngeal  nerves  were 
exposed  and  placed  on  shielded  electrodes.  The  nerves 
were  tied  just  above  the  electrodes,  in  order  to  prevent 
reflex  stoppage  of  the  respiration  on  irritation.  The  thy- 
roid and  cricoid  cartilages  were  next  exposed  without 
disturbing  any  muscular  attachment.  Two  levers,  twenty- 
eight  centimetres  in  length,  composed  of  ordinary  straw, 
and  terminating  at  one  end  in  a  strong  pin,  were  stuck  into 
the  centre  of  each  cartilage.  The  farther  end  of  each  lever, 
being  tipped  with  a  delicate  metallic  point,  was  so  arranged 
as  to  record  graphically  on  a  smoked  paper  of  a  revolving 


4 


F.    //.    HOOPER. 


cylinder  the  movements  of  the  cartilages  produced  by  irri- 
tating the  superior  laryngeal  nerves. 

Stimulation  was  produced  by  a  rapid  succession  of  induc- 
tion shocks  from  an  apparatus  graduated  empirically  by 
Pick's  method.  The  graduation  was  such  that  an  intensity 
of  i,ooo  corresponded  to  the  stimulation  produced  when  a 
secondary  coil  of  10,260  turns  of  fine  wire  was  pushed 
wholly  over  the  primary  coil.  After  repeated  trials,  it  was 
determined  that  an  intensity  of  fifteen  was  the  most  appli- 
cable to  the  purpose,  and  this  intensity  was,  therefore, 
employed  in  all  the  experiments. 

The  tracings  are  to  be  read  from  left  to  right.  The 
asterisk  denotes  the  beginning  of  the  stimulation,  the 
dagger  the  end. 


Thifroid 


Figl 


DOG   ETHERIZED  ;    SUP.    LARYNGEAL   NERVES   TIED. 

The  undulations  of  the  above  tracing  in  fig.  i  represent 
the  respiratory  movements  of  the  larynx.  At  the  point  of 
■*  stimulation,  it  will  be  noticed  that  the  cricoid  cartilage  was 
drawn  up  toward  the  thyroid,  as  indicated  by  the  marked 
rise  of  the  cricoid  curve.  As  soon  as  the  irritation  ceased, 
the  lever  immediately  fell  to  its  previous  level.     No  up- 


TENSION  OF   THE    VOCAL   BANDS. 


5 


ward  or  downward  movement  of  the  thyroid,  however,  can 
be  observed.  The  respirations  are  somewhat  shortened 
during  the  stimulation,  but  the  recording  pen  attached  to 
the  thyroid  cartilage  remains  on  the  same  level  throughout 
the  experiment.  The  next  experiment,  performed  after  the 
dog  had  been  killed  by  section  of  the  medulla  oblongata, 
yields  the  same  result. 


TigZ 


Thyroid 


^ 


r 


Cricoid. 


DOG  ;    MEDULLA    DESTROYED. 


In  this  figure  (2)  it  will  be  noted  that,  respiration  having 
ceased,  the  pens  trace  a  straight  line.  As  in  the  previous 
experiment  (fig.  i),  stimulation  of  the  nerves  caused  the 
same  rise  of  the  cricoid,  while  no  appreciable  effect  was  pro- 
duced on  the  thyroid.  The  minute  elevations  in  the  thyroid 
line,  at  the  points  of  irritation,  were  probably  accidental,  as 
will  be  explained  hereafter.  The  following  experiment  was 
performed  on  a  different  animal,  but  under  similar  condi- 
tions as  the  preceding. 

Here  (fig.  3)  the  same  effects  as  in  the  foregoing  experi- 
ments are  evident,  only  more  pronounced,  the  rise  of  the 
cricoid  being  very  powerful.  The  undulations  in  the  thyroid 
line  will  be  readily  understood  when  we  consider  what  an  in- 
finitely small  amount  of  movement  of  the  cartilage  would  be 


6  F.    11.    HOOPER. 

sufficient  to  produce  a  change  in  a  flexible  pen  at  the  end 
of  a  lever  of  the  length  used  in  these  researches.  Indeed, 
it  is  surprising  that  there  is  not  more  oscillation,  for,  the 
thyroid  not  being  absolutely  fixed,  the  contraction  of  the 
muscle  would  necessarily  cause  enough  motion  to  account 
for  the  slight  unevenness  of  the  thyroid  lines.  But  that 
there  is  no  positive  movement  imparted  to  the  thyroid  by 
the  action  of  the  muscle  seems  beyond  doubt. 


Thijrold 


Fig  3. 


Cricoid 


DOG  ;    MEDULLA    DESTROYED. 


These  experiments  were  repeated  many  times,  on  the 
same  and  different  dogs,  always  with  confirmatory  results. 
A  dissection  was  made  subsequently  in  every  instance,  in 
order  to  be  sure  that  the  electrodes  had  been  on  the  su- 
perior laryngeal  nerves, — a  necessary  precaution  in  such  in- 
vestigations. 

We  by  no  means  submit  these  researches  as  establishing 
the  entire  function  of  the  thyro-cricoid  muscle  ;  inasmuch  as 
this,  like  all  the  intrinsic  muscles  of  the  larynx,  has  the  impor- 
tant characteristic  of  being  arranged  or  divided  into  bundles 


TENSION  OF   THE    VOCAL   BANDS.  7 

of  fibres.  Under  what  conditions  these  bundles  act,  how 
they  act,  whether  they  can  act  separately  or  only  jointly,  is 
as  yet  undetermined.  Nevertheless,  the  salient  point  clear- 
ly demonstrated  by  our  experiments  is,  that  the  principal 
effect  of  the  contraction  of  the  muscle  is  to  draw  the  ante- 
rior portion  of  the  cricoid  cartilage  up  on  to  the  thyroid, 
the  latter  remaining  practically  fixed.  The  posterior  plate 
of  the  cricoid,  with  every  thing  attached  to  it,  being,  there- 
fore, rotated  downward  and  backward,  the  bands  are  neces- 
sarily stretched.  It  would  be  beyond  the  scope  of  this  paper, 
besides  leading  us  into  the  field  of  speculation,  to  discuss  the 
probable  working  of  the  different  bundles  of  the  muscle. 
But  it  is  not  improbable  that  the  vocal  bands,  being 
stretched  in  the  first  place  in  the  manner  described,  the 
oblique  bundles  may  then,  in  their  turn,  come  into  play, 
and  increase  the  tension  by  pulling  the  cricoid  cartilage  di- 
rectly backward.  When  we  bear  in  mind  that  (with  the 
exception  of  a  small  part  of  the  inferior  constrictor)  not  a 
single  extrinsic  muscle  is  attached  to  the  cricoid  cartilage, 
and  reflect  upon  the  mechanical  construction  of  the  larynx, 
it  is  difficult  to  comprehend  by  what  mechanism  it  can  pos- 
sibly be  fixed  in  a  sense  that  would  permit  the  thyroid  to 
be  pulled  down  upon  it.  Nature,  doubtless,  never  intended 
that  it  should  be.  On  the  contrary,  its  extreme  mobility  is 
one  of  its  most  striking  and  distinguishing  characteristics. 
In  vocalization  the  thyroid  cartilage,  steadied  by  the  pow- 
erful extrinsic  muscles  inserted  into  it,  may  be  regarded  (as 
compared  to  the  cricoid)  as  the  passive  agent,  while  the  lat- 
ter, owing  to  the  manner  in  which  it  swings  upon  the  short 
processes  of  the  thyroid  behind,  and  to  the  elasticity  of  the 
parts  in  front,  and  to  a  certain  extent  on  the  sides,  is  per- 
mitted to  play  upon  it  with  every  delicacy  of  adjustment 
through  he  agency  of  the  intrinsic  muscles  of  the  larynx 
attached  to  it,  and  of  another  force  presently  to  be  alluded 
to.  Indeed,  were  it  not  for  this  free  and  unrestrained  move- 
ment of  the  cricoid  cartilage  on  to  the  thyroid,  the  marvel- 
lous capabilities  possessed  by  certain  phenomenal  voices 
would  be  impossible.  For  to  it  the  stretching  of  the  vocal 
bands  is,  in  a  great  measure,  directly  due.     When  we  are 


8  F.    H.    HOOPER. 

told,'  by  J.  Solis-Cohen,  that  a  certain  singer,  with  a  compass 
of  three  octaves,  was  capable  of  effecting  as  many  as  two 
thousand  one  hundred  changes  of  pitch,  and  "that  the  va- 
riation of  tension  between  the  tones  that  she  could  produce 
would  represent  a  successive  lengthening  and  shortening  of 
the  vibrating  edges  of  the  vocal  bands  in  successive  propor. 
tions  of  one  seventeen-thousandth  of  an  inch,"  we  are  simply 
lost  in  astonishment.  It  is  therefore  interesting  to  inquire 
whether  muscular  action  is  the  only  agent  concerned  in 
effecting  such  extensive  as  well  as  delicate  adjustment  as 
this. 

Passing  now  to  our  second  series  of  experiments  we  shall 
attempt  to  point  out  another,  and  not  an  unimportant, 
factor  concerned  in  tightening  the  vocal  bands,  which,  act- 
ing independently  of  all  muscular  innervation,  exerts  its  in- 
fluence upon  the  cricoid  cartilage,  causing  a  movement  of  it 
identical  with  that  produced  by  the  action  of  the  tensor  just 
considered. 

ip)   THE  ACTION  OF  THE  EXPIRATORY  BLAST  OF  AIR. 

Hitherto  the  action  of  the  air-blast  as  a  tensor  of  the 
vocal  bands  has  been  recognized  as  producing  its  effect  (as 
any  current  of  air  might  stretch  an  elastic  membrane) 
merely  by  its  force  in  coming  in  contact  with  them.  But  it 
is  the  purpose  of  the  subjoined  experiments  to  establish  the 
fact,  that  in  addition  to  the  general  rise  of  the  whole  larynx, 
as  in  singing  high  notes,  the  pressure  of  air  causes  an 
excessive  and  independent  upward  movement  of  the 
cricoid  cartilage  on  to  the  thyroid,  of  which  no  mention,  to 
our  knowledge,  has  heretofore  been  made. 

The  method  adopted  in  arranging  the  dogs  was  as 
follows  : 

Having  been  thoroughly  etherized  during  the  early  part 
of  the  operation,  the  animal  was  subsequently  killed  by 
bleeding  and  section  of  the  medulla  oblongata.  The  thyroid 
and  cricoid  cartilages  were  first  exposed  by  a  careful  dissec- 
tion in  order  that  the  normal  position  of  the  external 
muscles  of  the  larynx  might  be  disturbed  as  little   as  pos- 

^  "  The  Throat  and  the  Voice,"  p.  105. 


TENSION  OF   THE    VOCAL   BANDS.  9 

■sible.  The  sternum  being  removed,  a  T-shaped  canula  was 
firmly  tied  into  the  trachea  very  near  the  base  of  the  lung. 
One  arm  of  the  canula  communicated  with  a  Fick's  man- 
ometer which  registered  the  pressure  of  the  air  blown  into  the 
trachea  through  the  other  arm  by  the  experimenter.  The 
larynx  being  nearly  closed  during  life  by  the  approximation 
of-  the  vocal  bands  in  phonation  or  in  singing  it  was  neces- 
sary in  some  way  to  imitate,  as  satisfactorily  as  possible,  the 
natural  condition  of  the  parts  by  closing  up  the  larynx. 
This  was  effected  by  a  pad  of  cotton-wool,  extending 
down  to  the  vocal  bands,  upon  which  a  small  quantity  of 
plaster  of  Paris  was  poured,  which  on  hardening  rendered 
the  larynx  sufificiently  tight  for  the  performance  of  the 
experiments.  The  same  levers  used  in  the  foregoing  ex- 
periments were  stuck  into  the  thyroid  and  cricoid  cartilages 
respectively  at  points  represented  in  the  drawing  by  black 
dots.  Advantage  was  also  taken  of  the  same  graphic 
method,  the  pens  tracing,  on  a  horizontal  revolving  cylinder 
bearing  a  smoked  paper,  the  curves  made  by  the  moving 
cartilages  under  the  pressure  of  the  column  of  air  coming 
from  the  trachea  below.  The  vertical  line  bearing  the  num- 
bers 20,  40,  50  represents  the  pressures  in  millimetres  of 
mercury,  the  Fick's  manometer  having  been  experimentally 
graduated.  The  dotted  lines  show  the  positions  of  the 
ascending  levers  attached  to  the  cartilages  at  corresponding 
pressures. 

The  arrow  indicates  the  direction  in  which  the  curves  are 
to  be  read. 

The  tracings  in  this  figure  (i)  were  obtained  by  inflation 
of  the  trachea  when  the  extrinsic  muscles  of  the  larynx  were 
intact.  A  glance  at  the  diagram  shows  that  at  equal 
pressures  the  rise  of  the  cricoid  curve  above  its  zero  line 
exceeds  that  of  the  thyroid.  By  measurement  we  have  at 
a  pressure  of  20  mm.  Hg.,  an  ascent  of  the  cricoid  lever  of 
8  millimetres,  while  that  of  the  thyroid  at  the  same 
pressure  is  7.  As  the  force  of  the  blast  of  air  is  in- 
creased, the  difference  is  more  marked.  At  a  pressure 
of  40  mm.  Hg.,  the  cricoid  moves  up  16  mm.,  the 
thyroid    10.5    mm.     At    a    pressure    of    50    mm.    Hg.,    the 


lO 


F.    H.    HOOPER. 


increase  is  still  greater.  Under  this  pressure  the  cricoid 
goes  up  19.5  mm.  to  12  mm.  of  the  thyroid.  At  all  pres- 
sures,  therefore,  in  this  experiment,  we  have  an  excess  of 
movement  of  the  cricoid  cartilage  over  that  of  the  thyroid. 


C>^c  cocJ. 


MUSCLES   INTACT. 


The  difference  in  the  height  of  the  curves  at  the  several 
pressures  being  i,  5.5,  7.5,  represents  in  millimetres  the 
approximation  of  the  cricoid  pen  to  that  of  the  thyroid, 
and  a  consequent  stretching  of  the  vocal  bands.  The 
amount  of  stretching  may  be  computed  by  dividing  this 
difference  by  the  ratio  of  the  length  of  the  lever  (28  cm)  to 
the  distance  from  the  vocal  process  to  the  crico-thyroid 
articulation  (16  mm.).  This  ratio  being  17.5  to  i  we  obtain 
a  lengthening  of  the  vocal  bands  of  about  .06  mm.,  at 
a  pressure  of  20  mm.  Hg.,  .31  mm.  at  40  mm.  Hg., 
and  .43  mm.  at  50  mm.  Hg. 


TENSION  OF   THE    VOCAL    BANDS. 


II 


In  order  to  determine  what  influence,  if  any,  the  extrinsic 
muscles  of  the  larynx  coming  from  the  sternum  and  attach- 
ed in  front  of  the  axis  of  rotation  of  these  cartilages,  would 
exert  upon  their  movements,  experiments  were  made  of 
blowing  up  the  trachea  after  section  of  the  sterno-hyoid  and 
sterno-thyroid  muscles  on  each  side.  The  accompanying 
diagrams  (reduced  about  one  third)  of  a  dissected  larynx  of 
one  of  the  dogs  used,  show  the  relation  of  the  parts  very 
clearly. 


LARYNX  OF  DOG.       FRONT  VIEW. 


//void. 


In  the  above  dissection  the  sterno-hyoidei  have  been  drawn 
slightly  apart  with  the  intention  of  exposing  the  anterior 
surface  of  the  thyroid  cartilage,  in  order  to  show  the  point 
of  insertion  of  the  lever.     In  the  following; 


12 


F.    H.    HOOPER 


SIDE  VIEW 


•loit 


ThufO  - 
Ayot'ct.  >Tv, 

Tesi.  crito 
arut.  m/. 

Crtco— 

tnuroicL 
Ciyiit.uio.iion. 


d.  m.. 


the  asterisk  marks  the  point  of  articulation  of  the  two  carti- 
lages. The  supposition  that  the  powerful  muscles  attached 
anteriorly  to  this  pivot  might  effect  the  movements  of  the 
cartilages,  was  sustained  by  the  following  experiments. 


Fia.Z. 


Cr-^co'iS. 


STERNO-HYOIUEI  CUT. 


TENSION   OF    THE    VOCAL   BANDS. 


13 


rlG.  3. 


STERNO-HYOIDEI  AND  STERNO-THYROIDEI  CUT. 

Inspection  of  these  curves  (figs.  2  and  3)  suffices  to  show 
the  increase  in  their  height  on  inflation,  after  the  depressor 
muscles  had  been  divided,  as  compared  with  fig.  i  when 
those  muscles  were  intact.  Their  relative  distances  in  num- 
bers at  the  different  pressures  may  be  best  appreciated  by 
the  following  table. 

FIG.  I. — MUSCLES  INTACT. 


Am't. 

of  pressure 

Movem't 

iMovem'i 

Difference,  representing 

Amt.    of    stretch- 

in mm 

.  Hg. 

of   cri- 

of thy- 

approximation    of     the 

ing  of    the  vocal 

coid  pen. 

roid  pen. 

cricoid    cartilage  to  the 
thyroid. 

bands  in  mm. 
(about) 

20 

8. 

7- 

I. 

.06 

40 

16. 

10.5 

5-5 

.31 

50 

19-5 

12. 

7.5 

•  43 

FIG.   2. — STERNO-HYOIDEI   CUT. 


20 
40 
50 


4- 
16. 

7- 
12.5 

22. 

15- 

-3- 

3-5 

7- 


—.17 
.20 
.40 


FIG.   3. — STERNO-HYOIDEI   AND  STERNO-THYROIDEI    CUT. 


20 
40 
50 


4-5 

4- 

17- 

15- 

27. 

21. 

1 

14  F.    II.    HOOPER. 

Ninety-two  experiments  of  this  character  were  recorded, 
which  were  performed  on  nine  different  dogs,  and  although 
the  general  results  corresponded  with  the  above  figures,  it 
must  be  admitted  they  were  not  invariably  uniform  in  regard 
to  the  effect  of  section  of  the  muscles.  The  discrepancies 
were,  however,  more  probably  owing  to  the  many  and  ob- 
vious difificulties  which  beset  the  complicated  nature  of  the 
experiments,  than  to  any  error  in  the  principles  involved. 
Not  presenting  them,  therefore,  as  being  scientifically  accu- 
rate, the  point  we  wish  especially  to  emphasize,  namely, 
the  greater  excursion  of  the  cricoid  cartilage  over  that  of 
the  thyroid,  was  evident,  and  we  think  the  following  facts 
may  be  said  to  have  been  established  : 

I.  At  higli  pressures  the  cricoid  cartilage  zV/T/^rz"^/;/;/ moved 
more  than  the  thyroid.  It  may  safely  be  asserted  that  at 
all  pressures  such  ought  to  be  the  result,  for  in  only  six  out 
of  the  ninety-two  experiments  was  the  thyroid  found  to 
have  made  a  larger  excursion  than  the  cricoid.  This,  in 
each  instance,  happened  at  the  lowest  pressure  ;  due, 
perchance,  to  some  minute  obstacle  on  the  revolving  cylin- 
der which  impeded  the  immediate  rise  of  the  pen,  or  to 
some  such  accidental  cause.  In  fig.  2,  at  the  low  pressure, 
it  will  be  observed  that  this  anomalous  movement  took 
place. 

II.  At  high  pressures,  after  section  of  the  muscles,  both 
cartilages  move  up  more  freely.  But  inasmuch  as  the  thy- 
roid rises  more,  in  proportion  to  the  cricoid,  than  when  the 
muscles  are  intact,  the  difference  between  the  curves,  it  will 
be  noted,  is  less,  and  consequently  also  the  stretching  of  the 
bands.  That  the  uncut  muscles,  therefore,  which  are 
attached  anteriorly  to  the  axis  of  rotation  of  these  cartilages 
should  restrain  their  motions,  to  some  degree,  especially 
that  of  the  thyroid,  seems  probable. 

It  is  evident,  then,  from  these  researches,  that  the  air 
escaping  from  the  lungs  produces  a  decided  upward  move- 
ment of  the  cricoid  cartilage,  in  addition  to  the  general 
rise  of  the  larynx,  which  movement  increases  in  propor- 
tion to  the  force  with  which  the  air  is  expelled  from  the 
chest. 


TENSION  OF    THE    VOCAL   BANDS.  15 

This  movement  may  be  readily  observed  by  taking  an 
excised  human  larynx  or  that  of  one  of  the  lower  animals, 
dog  or  cat,  and  arranging  it  in  this  manner.  Suspend  the 
larynx  to  an  ordinary  iron  holder  by  a  clamp  attached  to  the 
hyoid  bone.  Plug  the  glottis  with  cotton-wool  and  plaster. 
Inflation  of  the  trachea  causes  the  front  part  of  the  cricoid 
cartilage  to  rise  on  to  the  thyroid.  Easy  as  it  is  to  demon-, 
strate  this  phenomenon,  we  meet  with  a  difficult  problem  in 
proceeding  to  explain  the  cause  of  it.  It  seems  fair  to  infer 
that  from  the  anatomical  construction  of  the  larynx  the 
ascent  of  the  cricoid  must  be  an  active,  and  the  descent  a 
passive  movement.  For  when  the  parts  are  at  rest  physio- 
logically, the  attachment  of  the  cricoid  to  the  trachea 
and  the  strength  of  the  thyro-cricoid  ligament  would 
prevent  any  downward  movement  of  the  cricoid  cartilage 
per  se  ;  if  any  such  movement  did  take  place,  it  would  have 
to  be  shared  also  by  the  thyroid  cartilage  and  the  trachea. 
It  was  at  first  thought  that  the  trachea  itself,  stretched  and 
expanded  by  inflation,  would  push  the  cricoid  upward,  and 
thus  approximate  it  to  the  thyroid.  But  we  were  compelled 
to  abandon  this  view,  as  it  was  found  that,  after  cutting  the 
trachea  off  close  to  the  cricoid,  leaving  only  enough  (two 
rings)  to  attach  the  canula,  the  phenomenon  took  place  as 
before. 

It  was  then  suggested  that  the  force  arising  from  the 
communication  of  motion  of  the  current  of  air  passing  from 
the  trachea  into  the  laryngeal  cavity  might  communicate  its 
onward  motion  to  the  cricoid,  and  thus  raise  it  on  to  the 
thyroid.  The  non-resisting  and  elastic  crico-thyroid  mem- 
brane offering  no  obstacle  to  such  a  movement  of  the  cricoid 
cartilage,  while  the  ascent  of  the  thyroid  would  be  checked 
by  the  resistance  arising  from  the  approximation  of  the 
bands  inside,  and  the  influence  of  the  extrinsic  muscles  out- 
side. Not  being  thoroughly  satisfied,  however,  that  this 
explanation  solved  the  problem,  we  surmised  that  the  ex- 
pansion of  the  larynx  itself,  when  injlated,  might  play  an 
important  part  in  producing  the  phenomenon. 

The  construction  of  the  larynx  is  so  complicated,  it  is 
not  at  first  sight  clear  why  such  a  movement  as  we  have 


l6  F.    II.    IIOOFKR. 

described  should  be  caused  by  inflation,  for  when  the  cricoid 
cartilage  is  pulled  up  on  to  the  thyroid  (as  by  the  action  of 
the  thyro-cricoid  muscle)  the  vertical  dimensions  of  the 
larynx  are  diminished,  while  the  antero-posterior  dimen- 
sions arc  increased.  Whether  the  capacity  of  the  larynx  is 
increased  or  diminished  by  this  movement  cannot  well  be 
determined  a  priori.  Therefore  the  following  experiment 
was  made  in  order  to  ascertain  whether  an  upward  move- 
ment of  the  cricoid  cartilage  was  necessarily  associated 
with  an  increased  capacity  of  the  larynx. 

EXPERIMENT. 

Small  dog.  Curarized.  Artificial  respiration.  Pharynx 
plugged  with  cotton-wool  ;  a  cord  strongly  tied  around  the 
head  and  jaw  in  front  of  the  ears,  to  compress  the  cotton 
and  the  passages  leading  upward.  Trachea  divided  between 
second  and  third  rings.  A  tubulated  cork  secured  in  the 
upper  end,  connected  by  a  rubber  tube  with  a  delicate 
Marey's  drum,  whose  lever  indicates  for  every  millimetre  of 
excursion  a  certain  fraction  of  a  cubic  centimetre  of  change 
of  volume  (i  mm.  of  curve  =:  o.oi  cc.  of  volume).  Irritation 
of  the  thyro-cricoid  muscle  on  one  side  caused  a  descent  of 
the  lever  of  lo  mm.,  indicating  an  increase  of  the  capacity 
of  the  larynx  of  one  tenth  of  a  cubic  centimetre.  When 
both  thyro-cricoid  muscles  were  simultaneously  stimulated 
the  lever  went  down  15  mm.,  showing,  as  might  be  ex- 
pected, a  still  greater  increase  of  the  capacity  of  the  larynx, 
as  both  of  the  muscles  working  together  would  naturally 
produce  a  more  forcible  rise  of  the  cricoid  than  one  alone. 

It  may  be  questioned,  certainly,  how  far  an  experiment 
of  this  nature  can  be  applied  to  the  living  human  larynx,  or 
with  what  logical  justice  we  can  draw  conclusions  from  it. 
We  believe,  nevertheless,  and  we  shall  append  additional 
proof  to  sustain  our  opinion,  that  the  lumen  of  the  larynx 
is  enlarged  by  an  upward  movement  of  the  cricoid  cartilage, 
and  therefore  in  violent  phonic  efforts  the  cricoid,  owing  to 
the  expansion  of  the  larynx,  must  move  upon  the  thyroid 
in  such  a  way  as  to  stretch  the  bands,  since  by  so  doing  it 
increases  the  capacity  of  the  larynx. 


TENSION  OF   THE    VOCAL   BANDS.  1/ 

Inspection  of  the  dissected  human  larynx  enables  us  to 
see  that  the  distance  from  the  vocal  process  of  the  aryte- 
noid cartilage  to  the  crico-thyroid  articulation  is  greater 
than  the  distance  from  this  point  to  the  anterior  edge  of 
the  cricoid  cartilage.  The  pivot  then  being  at  the  articula- 
tion, the  long  arm  of  the  lever  is  above,  the  short  arm  in 
front  of  the  fulcrum.  The  diagram  herewith  presented, 
drawn  from  exact  measurements,  and  representing  the 
inside  of  the  right  lateral  half  of  a  human  larynx  from  which 
the  soft  parts  have  been  removed,  shows  us  at  a  glance  the 
relative  proportions  of  the  unequal  arms  of  the  lever.  The 
fulcrum,  denoted  by  the  black  dot,  is  directly  opposite  the 
crico-thyroid  articulation. 


Now  here  are  two  artificial  larynges  roughly  constructed 
to  illustrate  the  points  of  the  present  inquiry.  The  models 
are  composed  of  a  skeleton  of  wood,  enclosed  in  a  piece  of 
thin  rubber  tubing,  which  renders  them  air-tight,  with  the 
exception  of  a  small  opening  in  the  top,  into  which  a  glass 
tube  is  inserted.  For  convenience  of  description  they  may 
be  designated  as  Nos.  i  and  2.  No.  i  is  articulated  on  the 
principle  of  the  human  larynx,  namely,  with  the  short  arm 


1 8  F.    H.    HOOPER. 

of  the  lever  in  front  of  the  fulcrum.  Connecting  this  by 
means  of  the  rubber  tube  with  the  Marey's  drum,  and  imi- 
tating the  action  of  the  thyro-cricoid  muscle,  by  pushing 
the  cricoid  upward,  we  notice  a  fall  of  the  lever  denoting 
an  increase  in  the  capacity  of  the  model.  No.  2,  on  the 
other  hand,  is  articulated  in  such  a  manner  that  the  long 
arm  of  the  lever  is  in  front  of  the  pivot.  It  will  be  seen  in 
this  case  that,  in  making  the  same  movement,  the  lever  at- 
tached to  the  drum  will  ascend.  Now,  if  the  human  larynx 
were  constructed  on  this  principle,  it  is  evident  that  a  blast 
of  air  would,  by  increasing  the  capacity  of  the  larynx,  relax 
the  vocal  bands.  The  relaxation  being  due  in  such  a  case 
to  the  fact  that,  as  the  horizontal  arm  of  the  lever  is  longer, 
and  offers  a  larger  area  than  the  vertical  arm,  the  pressure 
of  the  air  inside  the  larynx  would  tend  to  force  the  former 
downward  rather  than  the  latter  backward.  The  dotted 
lines  in  the  following  two  cuts,  indicating  the  manner  the 
lever  would  move  in  the  two  instances,  make  our  reasoning 
clear.  No.  i  is  according  to  the  leverage  of  the  human 
larynx  ;  No.  2,  not.  The  line  a  b  represents  the  vocal 
band. 


>.  i 


/q.  1 


These  researches  may,  perhaps,  offer  a  suggestive  clue  in 
elucidating  certain  pathological  conditions.'  For  instance, 
the  fact  that  the  singing  voice  can  be  relied  upon,  while,  in 
the  same  individual,  conversation  is  impossible,  may,  per- 
chance, in  a  measure,  be  explained  by  this  action  of  the  air- 
blast   as  a  tensor  at  high  pressures.     We   know    that   the 


*  See  case  reported  by  Solis-Cohen:  "  Diseases  of  Throat,"  p.  642.  Ed.,  1880. 


TENSION  OF   THE    VOCAL   BANDS.  I9 

famous  singer,  Malibran,  was  always  at  constant  war  with 
her  rebellious  voice.  She  would  never  admit  that  it  could 
resist  her  ;  it  was  something  to  be  conquered.  And  it  is 
only  necessary  to  refer  to  the  interesting  pages  by  M.  Le- 
gouve  upon  this  remarkable  woman  to  learn  the  power  of  a 
strong  will  and  powerful  lungs  to  overcome  vocal  difficulties, 
and  how  she,  with  her  characteristic  saying,  "  I  will  force  it 
to  obey  me,"  was  able,  in  spite  of  severe  pharyngeal  inflam- 
mation, to  electrify  an  audience  solely  by  the  violence  of 
her  efforts.  It  is  insufficient  to  ascribe  such  vocal  feats  to 
"inspiration"  so-called.  There  can  be  no  vocal  effects 
produced  without  definite  physical  causes.  There  may  be 
many  which  are  not  demonstrable,  for  the  working  of  the 
intrinsic  muscles  of  the  larynx  is  so  complex  that  it  is 
doubtful  if  we  can  devise  any  means  of  investigation  suffi- 
ciently delicate  to  determine  accurately  all  the  laws  which 
regulate  their  marvellous  adjustments.  Experimentation 
on  one's  self,  af^ier  the  fashion  of  certain  writers,  by  push- 
ing the  cartilages  with  the  fingers  this  way  and  that,  pre- 
sumably imitating  the  action  of  some  muscle,  is  too  gross  a 
method  to  apply  to  such  a  delicate  apparatus  as  the  larynx  ; 
and  theories  founded  on  such  manipulations,  however  inter- 
esting, cannot  be  accepted  as  reliable.  To  insure  accuracy, 
the  nerve  supplying  the  muscle,  or  muscular  bundles,  ought 
\o  be  exposed  and  irritated,  and  the  working  of  the  fibres 
graphically  registered  in  some  such  manner  as  we  have 
attempted.  We  think  the  facts  demonstrated  by  these 
researches  justify  the  following  conclusions: 

I.  .The  cricoid  cartilage  is  the  most  movable  part  of  the 
laryngo-tracheal  tract. 

II.  The  thyro-cricoid  muscle,  according  to  its  physiologi- 
cal action,  should  be  described  as  arising  from  the  thyroid 
cartilage,  and  inserted  into,  and  giving  motion  to,  the  cri- 
coid. 

III.  The  air-blast,  in  virtue  of  the  mechanism  herein  set 
forth,  is  a  direct  and  important  longitudinal  tensor  of  the 
vocal  bands. 


20  F.    H.   HOOPER. 


BIBLIOGRAPHY. 

Galen:  "  Oeuvres  Anatomiques,  Physiologiques  et  Medicales."  Traduites 
par  le  Dr.  Ch.  Daremberg. 

Vesalius  :    "  De  Corporis  Humani  Fabrica,"  1545.    (Ed.  of  Albinus,  1725.) 

Casserius  :     "  De  Vocis  Auditusque  Organis,"  1601. 

Brown  :     "A  Compleat  Treatise  of  the  Muscles,"  1683. 

DioNis  :     "  Nouvelle  Anatomic  de  1'  Homme,"  1695. 

CowPER:     "  Myotomia  Reformata,"  1724. 

Haller  :     "  Elementa  Physiologiae,"  1766. 

Magendie  :  "  Memoire  sur  1'  usage  de  1'  Epiglotte  dans  la  Deglutition," 
Paris,  1 813. 

Willis:  Mechanism  of  the  Larynx.  Trans,  of  the  Camb.  Philosoph.  Soc, 
X,  iv,  1829. 

Lauth  :  Remarques  sur  la  Structure  du  Larynx,  etc.  Memoires  de  1'  Aca- 
demic Royale  de  Medecine  de  Paris,  Tome  iv,  1835. 

Longet  :  Rechcrchcs  Experimentales  sur  les  Nerfs  des  Muscles  du  Larynx, 
etc.     Gazette  Medicale  de  Paris,  1841. 

Theile:     "  Traite  de  Myologie  et  d'Angeiologie,"  1843. 

Bishop  :  Anatomy  of  Larynx,  in  Todd's  "  Cyclopaedia  of  Anat.  and  Phys.," 
1839-1S47. 

Ci;viER  :     "  Anatomic  Comparee,"  Tome  viii,  1846. 

Harless  :     Stimme  in  Wagner's  "  Handworterbuch  d.  Physiologic,"  Bd.  iv, 

1853. 

Battaille  :     "  Nouvelles  Recherches  sur  la  Phonation,"  1861. 

Budge  :     "  Lehrbuch  d.  speciellen  Phys.  des  Menschen,"  1862. 

Riegel  :  Lahmung  Einzelner  Kehlkopfmuskeln,  Deut.  Arch.  /.  klin. 
Med.,  Bd.  vii,  1870. 

Jelenffy  :     Der  Musculus  crico-thyreoideus.  Arch.  f.  d.  Ges.  Physiol.,  vii, 

1873. 

ScHECH  :  Experimentelle  Untersuchungen  Uber  die  Funktionen  der  Nerven 
und  Muskeln  des  Kehlkopfs,  Ztschr.  f.  Biologic,  ix,  1873. 

Schmidt  :     "  Die  Laryngoscopie  au  Thieren,"  1873. 

ROhlmann  :  Sitzungsb.  d.  Wiener  Acad.  Mathernnaturw.,  Classe  Ixix, 
1874. 

Michael:     Berlin,  klin.  IVochenschr.,  iSjd. 

Grutzxer  :     In  Hermann's  "  Handbuch  d.  Physiol.,"  1879. 

Meyer  :     ' '  Unserc  Sprachwerkzeuge,"  1880. 

Elsberg  :  Paral.  of  mus.  of  larynx.  Arch.  0/  Laryngology,  vol.  iii.  No.  3, 
1882. 

See  also  the  various  standard  text-books  of  anatomy  and  physiology ; 
special  works  on  diseases  of  the  throat  and  physiology  of  the  voice. 


Press  of 

G.  P.  Putnam's  Sons 

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